1. Field of the Invention
The invention relates to a process for selectively recovering thermoplastic polymers, and particularly polyester polymers from collections of yarns, films, fibers or fabrics, including dyed polyester fibers, for use in production of new undyed thermoplastic products, particularly polyester fibers, films and the like. More specifically, the invention relates to a process for selectively recovering polyester polymer by means of stripping the dye from dyed polyester fibers, subsequently dissolving the polyester fibers, separating the solution from any insoluble materials, and thereafter precipitating out the polyester polymer for reuse.
2. Prior Art
The consumption of thermoplastic polymers is greater than ten billion pounds per year. Some, such as polyethylene, polypropylene, polyvinylchloride, polystyrene, polyamides and polyester, surpass the billion pounds per year rate. The use of many of these relatively expensive thermoplastic polymers in synthetic fibers has also increased tremendously. It has been estimated that the world's consumption of synthetic fibers will reach some 12 million metric tons (26 billion pounds) by the year 1980, of which 4.6 million metric tons would constitute polyester fibers, 4.1 million metric tons would be polyamide fibers and 2.3 million metric tons will be polyacrylic fibers (Chemical and Engineering News, Feb. 2, 1970, p. 22).
Concomitantly the world is facing a shortage of raw materials for thermoplastic polymers; and sophisticated and efficient methods of recycling are needed.
Various methods have been described in the prior art for the recovery of thermoplastic polymers, including polyester polymers, from scrap polymer; and these include the dissolution of the polymer in various solvents; thereafter precipitating and recovering the polymer. The objects of such processes were to avoid polymer degradation and/or to separate from the usable polymer the degraded polymer and/or monomers as impurities. These processes were slow and expensive; suitable only for laboratory usage; moreover, they neither addressed themselves to nor did they solve fiber separation and dye removal problems.
Waste fibers, films, yarns and fabrics have been garnetted and reprocessed for various uses including the manufacture of yarn and fabrics.
A recent U.S. patent application discloses a generic concept for separation of collections of yarns and fabrics through solvent schemes, for successive dissolution of various constituents, and for recovery of polymers, but these were not specific to polyester recovery or to dyed polyester in the starting material and the speculatively described processes were slow, inefficient, expensive and therefor commercially impractical.
Neither the prior art fabric recovery processes nor the polymer recovery processes have provided for efficient dye stripping as well as fiber separation in conjunction with polymer recovery, and most have not addressed the problem.
It will thus be recognized that a satisfactory and efficient process for recovery of polyester polymer from collections of dyed fibers or fabrics also comprising cellulosic fibers and/or other man-made fibers, would be a meritorious advance in the art. It would substantially reduce the raw material requirement for the world's largest fiber market.